Deposits - Maturity Distribution of Time Certificates of Deposits (Details) $ in Thousands	Dec. 31, 2017 USD ($)
Maturity distribution of time certificates of deposit
Three months or less	$ 2,059,622
Over three through six months	937,267
Over six through twelve months	489,151
2019	297,636
2020	149,400
2021	139,039
2022	101,641
Thereafter	126
Total	4,173,882
Under $250,000
Maturity distribution of time certificates of deposit
Three months or less	327,392
Over three through six months	274,728
Over six through twelve months	215,994
2019	139,981
2020	103,416
2021	99,475
2022	62,351
Thereafter	126
Total	1,223,463
$250,000 or More
Maturity distribution of time certificates of deposit
Three months or less	1,732,230
Over three through six months	662,539
Over six through twelve months	273,157
2019	157,655
2020	45,984
2021	39,564
2022	39,290
Total	$ 2,950,419